Embodiments of the invention relate to a method and an apparatus for generating an electrode stimulation signal in a neural auditory prosthesis. In embodiments of the invention, a randomizer is controlling a generation of the electrode stimulation signal to vary in a random manner within a certain allowable range.
The field of the present invention relates to an auditory prosthesis, like a cochlear implant or a brainstem implant, configured for delivery of non-simultaneous stimulation through at least two active electrodes.
The global deaf population is roughly estimated to be 0.1% of the total population. There are various causes of deafness including infectious, traumatic, toxic, age-related, occupational, and genetic disorders. In the majority of the cases the inner ear, i.e. the cochlear structure, is damaged.
Nowadays, however, there are ways to bypass the peripheral auditory system and directly stimulate auditory nerve fibers. This process is made available by the cochlear implants (CIs), which have been the target of intensive research for over fifty years by now, and by the more recent brainstem implants (BIs). Even though cochlear implants are the most successful neural prosthesis ever, hearing can only be partially restored by them. Patients achieve an average of almost 80% in speech recognition tests under quiet conditions (without lip-reading) until the end of the second year after implantation (cf. the article “Evidence that cochlear-implanted deaf patients are better multisensory integrators” by Rouger et al., published in Proc. Nat. Acad. of Sciences (PMAS), vol. 104 (17), pp. 7295-7300, 2007 and in Journal of Acoust. Soc. Am., vol. 111 (5), Pt. 1, May 2002), but most cochlear implant recipients remain unable to enjoy music or to distinguish among complex sounds. Moreover, speech recognition in noisy environments is still a challenge for most cochlear implant recipients.
Even today a number of modern CI systems employ speech processing strategies that are still based on very “simple” filter-banks (e.g. the Fast Fourier Transform (FFT), dating back to the mid-1960s) to mimic the complex functionality of the human auditory system. On the other hand, numerous biologically motivated models of the basilar membrane (BM, organ of the cochlear filtering) and of auditory structures—having strong non-linear properties beyond the BM have been developed during the last 20 years.
Recent research of the inventor indicates that time has come for practical CI/BI systems and theoretical ear models to converge and facilitate a higher quality of restoration of hearing.
U.S. Patent Application Publication No. 2009/0030486 A1 discloses a method of generating a control signal for a cochlear implant based on an audio signal. An activity pattern over time at a plurality of inner ear cells of an auditory model is calculated. Activity events within the activity pattern are filtered out based on a recognition of a characteristic pattern in the activity pattern, whereby cleared information is obtained. The cleared information is further used as a control signal for the cochlear implant, or the control signal for the cochlear implant is derived from the cleared information. The idea disclosed in the '486 U.S. patent application is based on the knowledge that in an activity pattern, a multitude of activity impulses is present at a plurality of inner ear cells of an auditory model over a time, which are not relevant for a patient's auditory sensation. Thus, a characteristic pattern in the nerve activity pattern can be recognized and, based on the recognition of the characteristic pattern, some of the activity events can be filtered out because they are only of secondary importance for a patient's perception. An example of the recognition of the characteristic pattern is a Hough-based pattern classification.
A hearing prosthesis configured for delivery of stochastic stimulation to a recipient is disclosed in U.S. Patent Application Publication No. 2009/0319005 A1. A stochastic stimulation generator is configured to generate a stochastic sequence of stimulation pulses having first and second inter-pulse intervals distributed stochastically throughout the sequence within controlled limits. Thus, the temporal positions of the stimulation pulses are subject to random variations, but the basic shape of a stimulation pulse is predetermined.
U.S. Patent Application Publication No. 2008/0319509 A1 discloses a similar approach as the '005 U.S. Patent Application Publication. In US 2008/0319509 A1 a binaural stimulation in a neural auditory prosthesis or hearing aid is disclosed. A phase jitter component is added to the binaural stimulation signal to reduce the periodic characteristics of the fine structure component by preserving the interaural time difference (ITD) information. Again, the temporal position of the basic pulses is varied at random, while a shape of each basic pulse remains constant.